CHAPTER I 

 BIMUNITY IN UNICELLULAR ORGANISMS 



Infective diseases of unicellular organisms. — Intracellular digestion in the Protozoa. — [13] 

 Anioebo-diastase. — Part played by digestion in the defence of the Protozoa 

 against infective parasites. — Defences of the Para7naecia against micro-organisms. 

 Part played by irritability in defence in the lower organisms, 

 munity of unicellular organisms to toxins. — Acclimatisation of Bacteria to toxic 

 substances. — Protective secretion of membranes by Bacteria, 

 'daptation of the Protozoa to saline solutions — of yeasts to poisons — of yeasts 

 to milk-sugar. 

 Irritability of unicellular organisms and Weber- Fechner's psycho-physical law. 



It 



The immunity of unicellular organisms against infective diseases and 

 against toxic agents is as yet very imperfectly understood. Never- 

 theless, it will be very useful for us to begin our study of the problem 

 of immunity on these lower organisms, because of their greater 

 general simplicity. It may be affirmed that if the line of comparative 

 pathology had been followed in our study of the etiology of diseases 

 of man and the higher animals, the parasitic nature of these infections 

 would have been established considerably earlier than was the case. 

 Thus, at a period when medical men and veterinary surgeons were 

 content to record the presence of Bacteria in the blood of their 

 patients, without attributing to them the slightest etiological rokf 

 botanists and zoologists had already proved most definitely that 

 many plants and lower animals were subject to epidemic diseases 

 undoubtedly set up by the parasitism of various exceedingly simple 

 organisms. In the same year, 1855, that Pollender^ published his fii*st 

 observations on the bacterium found in the blood of animals afiected 

 by anthrax though he could not trace the slightest relation between 

 the presence of this organism and the etiology of the disease, the 



1 Vrtljschr. f. gerichtl. Med., Berlin, 1855, S. lOZ 



