44 



TRANSACTIONS AND PROCEEDINGS OF THE [Sess. lv. 



Dependent upon the temperature of the room in which 

 the medium is placed, we shall further find that its strength, 

 as regards the gelatigenous power, will be subject to great 

 modification. With us here we find that in the winter a 5 

 per cent, gelatine is quite as firm as is a 7'5 gelatine in the 

 summer. If, however, one goes farther south, the gelatine 



Fig. 4. 



Fig. 5. 



Diagrams illustrating the gi'owtli of FneiimococcKS in gelatine of varying 

 density. Fig. 4 in 5 per cent. ; Fig. 5 in 10 per cent. 



must be increased in order to obtain firmness. Thus, as the 

 form of growth varies in relation to the gelatigenous density, 

 if an observer cultivated the Bacillus arhGrescens in a very- 

 warm climate, in a 10 per cent, gelatine, he should obtain 

 an arborescent growtli. If such a growth was then descriljed 

 as obtained in a medium of that density, and if one obtained 

 similar material and attempted to corroborate the observer's 

 description working in this country, then it is self-evident 

 that his attempts would end in failure, owing to the fact 

 that in our country a 5 per cent, gelatine is just as firm as 

 a 10 per cent, gelatine in a warmer country. 



Such oljservations show to us tiie absolute necessity not 

 only of carefully recording the nature of the medium with 

 which our work is made, but also of registering most accur- 



