NUTRIENT SOLUTIONS. 123 



quently meat extract behaves as an acid towards both blue litmus 

 and phenolphthalein. As a general rule, 10 c.c. of this broth 

 require an addition of 1.8 c.c. of deci-normal alkali to prevent the 

 colour change from taking place with blue litmus, and an addition 

 of 3 c.c. to enable it just to redden phenolphthalein. This acid 

 reaction of meat-broth being a hindrance to the development of 

 many bacteria, it is on that account rendered very sliylitly alkaline, 

 the resulting liquid containing a smaller or larger percentage of 

 alkali according to the indicator used, and which should be selected 

 in accordance with the requirements exacted of the medium in 

 each case. After neutralisation, i per cent, of dry peptone and 

 a J per cent, of common salt are added to the liquid, which is 

 then boiled again for a quarter of an hour (but not longer), and 

 filtered hot; the resulting liquid, generally known as nutrient 

 bouillon, is filled into small bottles (e.g. 5-10 c.c.) and sterilised 

 by either a thrice-repeated treatment in the steamer or once under 

 pressure. 



When, under particular circumstances, suitable meat cannot 

 be obtained, meat extract is used instead. Hueppe's formula for 

 making meat-extract bouillon is : 30 grms. dry peptone, 5 grms. 

 grape-sugar, and 5 grms. meat extract, dissolved in i litre water, 

 and boiled, filtered, and neutralised as previously described. The 

 sterilisation of the (once more boiled and filtered) bouillon must 

 be performed with scrupulous care, the meat extract being rich 

 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 albu- 

 minoid matters was first observed by DUJARDIN (I.) in. 1841, in. 

 the case of a fission fungus allied to Bacterium termo, and was 

 afterwards decisively proved, as regards the zymogenic fungi, by 

 Pasteur. In 1893 USCHINSKY (I.) demonstrated that the majority 

 of pathogenic bacteria (of typhus, cholera, diphtheria, tetanus,, 

 swine-erysipelas, &c.) could also be cultivated in a liquid contain- 

 ing 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 toxins (which are probably allied to the albumoses and 

 peptones) can also be elaborated in non-albuminous media proves 

 that they are not derivatives of albumin, but are the result of 

 synthetical processes occasioned by the vital activity of the- 

 organisms. 



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

 PROSKAUER and BECK (I.), C. FRAENKEL (II.), and others. Since- 



