Immunity in Unicellular Organisms 23 



quite a series of such envelopes (Fig. 5), thus coming to resemble 

 a palmellaceous Alga surrounded by successive layers of membranes 

 or certain other vegetable cells whose principal means of defence 

 against all kinds of injurious influences consists in the production 

 of these protective membranes. 



Fig. 4. Another tubercle bacillus Fig. 5. Tubercle bacillus surrounded 



surrounded by two membranes. by a series of concentric layers. 



Quite recently Trommsdorf 1 , in Buchner's laboratory in Munich, 

 has carried out a series of experiments on the adaptation of 

 the cholera vibrio and of the typhoid bacillus to the bactericidal 

 substance found in the blood of the rabbit. He has been able to 

 confirm the results of his predecessors and by various experiments 

 has convinced himself that these two micro-organisms are capable 

 of adapting themselves to existence in the defibrinated blood and in [26] 

 the blood-serum of the rabbit. 



The immunity, or acclimatisation of injurious organisms to different 

 toxins, presents an undoubted analogy to the phenomena of adaptation 

 shown by these organisms to mineral or organic poisons. It has long 

 been known that the same species of Protozoa are met with in both 

 fresh and salt water and that it is possible to gradually accustom 

 Infusoria and Amoebae to tolerate an amount of sea salt which at first 

 is absolutely fatal to them. This toleration is not acquired unless care 

 be taken to increase the amount of salt very gradually : too abrupt a 

 rise inevitably causing death. By this means Cohn' 2 accustomed the 



1 Arch.f. Hyg., Miinchen u. Leipzig, 1900, Bd. xxxix, S. 31. 



2 " Entwickelungsgeschichte der mikroskopischen Algen und Pilze," Nov. Acta 

 Acad. Goes. Leap. Carol., 1854, t. xxiv, p. 1. 



