1 06 Fermentation and Kindred Phenomena. 



death. The blood of the animals thus infected is full of 

 micrococci, and these can be cultivated by the ordinary methods. 

 The virulence of saliva differs considerably in different indi- 

 viduals. 



Action of disease organisms. — Many questions arise from the 

 discovery of the connection between organisms and disease, 

 especially regarding the nature of their action upon the system. 

 It has been definitely proved, as I have explained, that many 

 species produce in the nourishing medium definite chemical 

 substances, some of which are excessively poisonous. Are the 

 diseases which are believed to be caused by organisms due to 

 the production of such poisons within the body ; or are the 

 blood and other secretions so altered in the nature as to be 

 unfit for the proper performance of their functions ; or are the 

 diseases caused by a merely mechanical action of the organisms 

 in plugging the minute blood vessels, and thus interfering with 

 circulation ? In fact, do the organisms act chemically or 

 mechanically ? 



I do not see how these questions can be definitely answered 

 until the chemist submits them to a very searching experimental 

 enquiry. He ought, in the first place, to investigate the chemical 

 action of each disease organism ; to grow them in various 

 nutrient media, and to investigate the nature of the substances 

 they give rise to in each case. If such substances, when freed 

 from the organisms which produce them, are found, when 

 injected into healthy animals, to cause similar effects to those 

 produced by the diseases themselves, the question will be 

 decided. 



There is an indication at least, if nothing more, that in certain 

 diseases it is the virus produced by the organism which acts, 

 and not the organism itself. Thus in spleen fever it often 

 happens that death is so rapid that only few bacilli occur in the 

 blood — quite too few either to cause the plugging of the small 

 vessels or to remove the oxygen from the blood, and thus to 

 deprive the system of that element. 



Recovery from disease. — Another question which presents 

 itself to our minds is this— How is it that if an infectious disease 



