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
