Introduction to the study of the mould-fungi parasitic on man
Roberts, Hugh Leslie
During recent years the attention of Bacteriologists has been directed by the discovery of certain facts to the question of racial variations in the lower and higher pathogenic fungi. It was steadfastly held by the founders of Bacteriology that the individuals of a species uniformly presented, under all circumstances, the type characters of the species; and when these individuals were associated etiologically with certain diseases, they were described as fixed forms. When deviations in form were met with in the same, or closely allied diseases they were categorically put down as new species. Tulasne, for the first time, pointed out the possibility of pleomorphism and he demonstrated that many forms which were currently described as distinct species were in reality merely different stages of development of the same individual. But the value of his discovery and its bearings on the problems of pathology were not recognised for many years, till the recent, greatly enlarged, cultivation of the pathogenic fungi, brought into prominence the fact that the individuals of the several pathogenic species presented astonishing differences under cultivation. When reared side by side in a common soil there are often marked physical differences, sometimes in the matter of colour, or growth-energy ; and when the inquiry is pushed still further, aided by the microscope, minuter, but still characteristic, variations may be discovered, such as alterations in the shape of the cell-elements, or fruit-bearing organs. Sometimes marked differences of another sort are discovered, such as the kind or degree of modification impressed on the soil by the growth of the fungus. If the soil is gelatinous, one individual may liquify the gelatine, while another may not, although both specimens may be, undoubtedly, members of the same species. Many instances might be drawn from the recent study of the lower fungi to illustrate this principle, and in an excellent paper by Adami,* the bacteriologist who doubt its truth may find for his consideration a large collection of well arranged examples. No one who has cultivated the moulds, which are pathogenic on man, on a sufficiently large and extensive scale, collecting his specimens from different countries, can fail to be impressed with the same truth. Fungi-culture has taught us that these Cryptogams are no exception to that general principle that Plants are specially liable to variation under cultivation, a principle which was illustrated by Darwin, in his own masterly style, in his work on "Animals and Plants under Domestication," but, in spite of which, many observers and bacteriologists have worked as if it had never been written at all. It is part of the object of this Thesis to show how wide is the range of these variations, and how differences, perhaps worthy of being considered racial, may be originated by changes in the conditions of cultivation. Extreme caution is needed when we come to deduce inferences; for every step we take into this new field of inquiry may discover facts which may cause us to modify, or even abandon, a previous conclusion. Now we are only at the verge of the unknown and this Thesis is offered as a contribution to aid us forward more by suggestions of facts than by demonstrated .conclusions.