Observations on some outstanding features of protozoan life

Abstract

The following pages represent for the most part the results of two summers' work under Mr. Sedgwick at Cambridge. In this place I would record my grateful indebtedness to that gentleman , not only for the ample provision - from a room down to the smallest necessary - put at my disposal , but also for the kindly encouragement and stimulus that are now associated in my mind with his name. Nor do I forget the interest and help accorded by Messrs Shipley and Graham Kerr.Proceeding on the assumption that since the daughter forms produced as the result of binary fission were duplicates , we need not look for any variation there, I endeavoured in the first instance to carry out e suggestion of Mr. Sedgwick's which he ultimately published in his presidential address to the Zoological Section of the British Association in 1899 , and laid plans under his direction to find out bi observation of the external characters how much variation could be detected in exconjugates as the result of conjugation by comparing them before and after the process. For this purpose it was necessary to choose a Ciliate with well- marked characters , and Stylonichia pustulata with its systems of cirri and membranellae appeared to offer the necessary requisite. The only line along which it seemed that I could work was to draw the creatures as accurately as was possible just before conjugation, repeat this after they had come out of conjugation, and then deduce results from measurements and other comparison of the drawings. The first difficulty was to get the creatures quiet so as to enable one to carry out this programme. A common method of quieting Protozoa is by pressure with a coverglass , but the distortion and displacement connected with this method rendered it impossible for the work in hand. Another method that has long been recommended is entanglement with cotton wool , but here the success that one obtains is distinctly limited and insufficient for the purpose. Cocaine and other narcotics have been faintly recommended: I have tried the former , but it not only did not produce the amount of quiet that was desirable , but it seemed to disturb the after-life of the creature. After many attempts with various agents , I found that a drop or so of a 4 per cent solution of gelatine had the effect of slowing down these Ciliata they even had frequent spells of absolute rest , except for the occasional movement of a cirrus. Accordingly eight well-marked specimens , all differing in size , were selected from a culture of Stylonichia , of which some members had alread.; entered into conjugation. They were then drawn after being, stilled by gelatine , and as they were easily recognisable , they were all put together in a watch -glass containing water from the original medium. Not a single case of conjugation occurred. I then took other specimens and subjected them to the gelatine medium for the same interval of time as was required to draw the others - each about a quarter of an hour or twenty minutes - and then re- transferred them to a watch-glass also containing water from the original culture. Again I had no success in conjugation: it would appear that the short sojourn in the gelatine was quite sufficient to change the peculiar bodily equilibrium that must be associated with the stage previous to conjugation. I have little doubt that a similar result would have attended all attempts with narcotics. Accordingly although working all the while at other points I had to acknowledge defeat in this particular instance.It was , however , while making these more careful examinations of individual forms that I came to doubt the initial assumption upon which one had been proceeding. Observation of a dividing Paramecium with a cleft tail suggested that even though the case was abnormal there was no reason why the products of binary fission should be exactly alike, unless indeed to afford theorists a rationale of conjugation. In several cases I observed that actually it was not the case, but drawings of these, poor in themselves, might unconsciously suggest that they represented theory rather than fact. Accordingly it seemed worth while to see what could be done by micro-photography, and although I was assured by a young scientific photographer that it was impossible to photograph living Ciliarta, an attempt was made. As I am not aware that living Protozoa - Ciliata at any rate - have been photographed before, I have added one or two pictures of forms that otherwise have no definite connection with the point to be illustrated. Ordinary Ilford chromatic plates were used , as also a Leitz 3 lens , which with the associated extension gave a magnification of about 80: the pictures were all taken instantaneously by incandescent light. Those that are offered are but a few successes out of about two hundred failures. The chief difficulty was in obtaining a cell small enough to be wholly included within the magnification of the lens. Ultimately a block of soft paraffin was employed in which a hole was pierced with a fine needle: it was then sectioned with the microtome , and in this way , by regulating the thinness of the section , a cell was obtained with the minimum of water in which the infusorian could live and yet be in focus all the time. A cover -glass was then super-imposed , and as it was held in position by a generous application of vaseline round the edge , we were enabled to take the photographs in a horizontal position They were taken at the Laboratory of the Royal College of Physicians with the kindly assistance of Mr. Hume Patterson.With regard to the remaining methods not much need be said. In pursuing the investigations relating to binary fission I employed damp chambers , constructed very much upon Maupas' system. In killing Protozoa I have pursued all the better known methods sale, many that are less known , but I have found nothing so satisfactory as the vapour of 2 per cent osmium, although good results were sometimes obtained with a formula given by Hoyer in the Archiv für Mikroscopische Anatomie , Vol.54:Part I - viz. one volume of 5 p.c. corrosive sublimate added to 2 volumes of 3 p.c. bichromate of potash.For the high-pcwer examination of living Ciliata I often made use of Professor Marshall Ward's culture tubes which can also be converted into very excellent miniature damp chambers. It at least seems a more natural state of affairs to have the living Protozoan in a drop , suspended from a cover-glass attached to one of these culture tubes than to have it prisoned and pressed under a cover-glass, however supported.Part I of this thesis contains some observations upon the intimate stricture of Protozoa , as deduced from sections longitudinal and transverse of Spirostomum ambiguum and Stylonichia pustulata. Part II consists of two sections. The first contains confirmation of Scheel's observations upon the sporulation of Amoeba proteus. The second contains an incomplete account of another method of reproduction which I have ventured to call Fragmentation. It may be regarded as a preliminary account in which the main steps are given: certain of the details have however yet to be ascertained. The main contention of the thesis will be found in Part III. It is only recently that Maupas' classical studies on the rationale of binary fission and conjugation have been called in question. I have attempted to go over his work in part , and while on the whole I find myself in agreement with him as against his critic Joukowsky , I venture to offer a few modifications in some details. To this part is appended some evidence for my belief that binary fission is not duplication. To prove this thoroughly would be the work of many months. At the sate time that work would only be multiplication and amplification of the data that I offer. In the second section of this part some notes upon conjugation are inserted. Part IV contains a short account of Encystment as it occurs amongst the Ciliata , together with descriptions of the little known cysts of Parameciur.? and Spirostomum.The attempted diagrams and photographs are well-nigh self-explanatory. The former were made with Abbe's drawing - apparatus: the methods adopted in connection with the microphotography have already been described. Much of the latter is sadly lacking in definition , but it is a matter of extreme difficulty to calculate and adapt that amount of water in the cell which is sufficient for the free movement and life of the Protozoan and yet not too great to allow it to get out of focus during the exposure. We may however hope for still better success in future attempts.