96 METHODS OF PUIK CIJLTURK 



in bacterial spores which are very tenacious of life. If this or the previously 

 described bouillon refuses to filter clear, the white of an egg, previously beaten 

 to a froth, is added, and the whole warmed up, boiled, and filtered, whereupon 

 the liquid will run through bright. 



The power of thriving in a solution of salts devoid of albuminoid matters 

 was first observed by DUJARDIN (I.) in 1841, in the case of a fission fungus 

 allied to flacteriitn ;md was afterwards decisively proved, as regards the 



/.ymogenic fungi, by Pasteur. In 1893 USCIIINSKV ([.) demonstrated that the 

 majority of pathogenic bacteria (of typhus, cholera, diphtheria, tetanus, swine- 

 erysipelas, <kc.) could also be cultivated in a liquid containing ammonium lactate 

 and sodium asparaginate as its sole supplies of nitrogenous nutriment. Cultures 

 in such media are specially suitable for the study of the poisonous substances 

 (toxins) excreted by these originators of disease, the separation of the former 

 being easy on account of the absence of albuminoids. The fact that these 



us (which ar probably allied to the albumoses and peptones) can also be 

 elaborated in non-albuminous media proves that they are not derivatives of 

 albumen, but are the result of synthetical processes occasioned by the vital 

 activity of the organisms. 



This matter has been investigated by FERMI and SCIIWKIMTZ (I.), PROSKAUER 

 and BECK (I.), C. FRAENKEL (II.), and others. Since bacteria rapidly increase 

 in such a solution, they are therefore also endowed with the faculty of effecting 

 the synthesis of albumen. Comparative researches instituted by E. CRAMER (II.) 

 with cholera vibrio showed, however, that the percentage content of albumen 

 (calculated to dry substance) in the cells cultivated in Uschinsky's solution is 

 lower than in the case of cultures grown in media containing albumen. 



In the sixth and seventh decades of the present (nineteenth) century the 

 preparation of a medium suitable as a universal nutrient medium for all possible 

 bacteria formed the object of the repeated exertions of many bacteriolo^i 

 Such an attempt is now regarded as hopeless on account of the knowledge which 

 has been gained of the very opposite conditions governing the vitality of the 

 several species. 



$ 83. The Dilution Method and Fractional Cultivation. 



It has already been remarked in chapter viii. that it is quite the exception 

 for a natural bacterial growth to consist of merely a single species, but that, as 

 a rule, we have to deal with a mixture of several. To separate these from one 

 another, and to further multiply each species by itself, so as to obtain therefrom 

 a pure culture, forms the aim of the methods of pure cultivation. 



We start with the assumption that we have to deal with a number of 



different bacteria inhabiting a liquid, inasmuch as there is a second condition 



ible, i.e. when the organisms are distributed within a solid body (Mich as 



cheese, butter, soil, A:C.). In the latter case a finely divided suffusion of the 



I 1. mu-t be made with sterilised water and treated in the same manner as 

 liquid bacterial samples. 



Very often the mycologist is set the task of determining the germ content, 

 i.e. ascertaining how many individual cells are contained per unit of space in a 

 sample. This contingency is often met with in fermentation experiments with 

 ii order that, from the result of the counting, the extent of the cell 

 multiplication occurring during the fermentation maybe ascertained. For such 

 purposes a so-called counting chamber, such as supplied, e.g., by Carl Zeiss of 

 Jena, is used. The arrangement of this appliance is shown in Fig. 32, in plan 

 at A and in vertical section at U. On a thick ^lass slide there is mounted a 

 cover glass (a) with a circular hollow, within which is cemented a second glass 



