THE PRODUCTS OF THE TISSUE CHANGE. 565 



the formation of peptonising ferments, or the specific 

 fermentations, so constantly accompany the same species 

 of organism that we can employ these facts as diag- 

 nostic means for distinguishing and recognising the 

 species. In the diagnostic key given above the possi- 

 bility of peptonising gelatine and the production of 

 pigment form a basis for the differentiation of bacteria 

 otherwise very difficult to distinguish from each other. 



Even when, under the influence of abnormal external 

 conditions, these characteristic products, and along with 

 them the most important means of recognising the 

 species of bacterium, have disappeared, the property of 

 the fungus in question can still be always regained as 

 soon as it is cultivated under those conditions under 

 which this property is usually observed. For even when Eetention of 

 the temporary unfavourable conditions were so abnormal evS^after the 



that some of the individuals died, or were pathologi- action of hurt- 

 . . .,..,, fnl influences. 



cally altered, it usually happens that if any individuals 



retain their power of development, the same products of 

 tissue change which are normally observed constantly 

 reappear under the same normal conditions. The 

 bacteria evidently behave in this respect as a whole like 

 the higher plants, which do not acquire or lose the 

 power of producing this or that specific product of 

 tissue change ; the hemlock, indeed, loses its power of 

 producing conium, and the plants which furnish indigo 

 cease to prepare indigo, when they lead a morbid exis- 

 tence under abnormal conditions, but both these func- 

 tions are resumed when more favourable conditions 

 permit the surviving examples or their offspring to 

 exercise fully their vital functions, and thus under all 

 circumstances this power remains as a specific property 

 of each specific species. It is only with regard to some With regard 

 of the properties of the lower fungi, viz., the production tfon^f fermen- 

 of fermentation or disease, that there is a peculiar tation and 

 deviation from the behaviour of the higher plants ; the 

 fission fungi may permanently lose these properties 

 under the action of abnormal external conditions, and 

 this loss may then be transmitted to the offspring 

 through a number of generations even when the con- 



