12 CULTURAL STUDIES OF SPECIES OF PENICILLIUM. 



attribute used in specific description has been shown to be a reaction 

 to environment, hence changeable with such environment (for some 

 species at least). Exhaustive study of all the species would be 

 endless. 



The alternative is to select certain media and a particular set of 

 conditions, then to cultivate all the organisms under investigation 

 in a uniform manner and to base distinctions of species upon differ- 

 ences in the reactions obtained, and upon the differing characters of 

 the several species, in this common environment. 



To test the reliability of such data, species obtained in the dairy 

 laboratories were first studied carefully upon the peptone-milk-sugar 

 gelatin described by Conn 4 and upon potato agar as described in 

 our previous bulletin (Thorn, 25 p. 7). From these cultures trans- 

 fers have been made to media of very different composition — Cohn's 

 solution, Raulin's fluid, milk in various forms, synthetic fluids pre- 

 senting different sources of carbon — alwa}'s bringing cultures back 

 to the original media. Many species differ so materially in gross 

 characters when grown upon these different media that successive 

 cultures, if not known to be pure transfers, might be supposed to 

 be different species; but when returned to the original media and 

 conditions these forms have immediately produced the characters 

 and reactions first found, with a large degree of uniformity. Abso- 

 lutely uniform reactions are not to be expected from living organ- 

 isms, at any rate under our imperfect control of working conditions; 

 but when such reactions are definitely recognizable as essentially 

 the same, the result may be judged as satisfactory. It is even more 

 confusing to find that two or more species may react very similarly 

 upon a particular substratum. A transfer of these organisms to a 

 medium of markedly different composition brings out the contrasting 

 characters, however. The desirability of recording the widest pos- 

 sible distinctions in such descriptive work makes necessary the use 

 of media differing in composition as much as practicable, in such 

 comparative cultures. 



It is worthy of note that the species P. roqueforti and P. camemherti, 

 essential to the cheese industry, have been isolated repeatedly from 

 cheeses of widely different origin. The Roquefort species has been 

 obtained from laboratories not concerned with Roquefort cheese 

 studies, from ensilage, and from other substances. The same char- 

 acters have been found in cultures of these two species from these 

 variable sources under conditions in which the possibility of close 

 genetic connection between cultures is thus remote. There seems to 

 be little possibility of question that these species at least are well- 

 fixed conidia-bearing forms, not cultural varieties of other species. 

 The question at issue was not whether or how variations could be 

 produced, but whether a particular variation is constantly produced 



