98 MICROBES AND TOXINS 



to sensitise plates towards rays which alone are chemically 

 inactive. They exert the same action on ferments and on the 

 toxins and anti-toxins of tetanus and diphtheria. This action 

 is entirely due to oxidation and only takes place when oxygen 

 is dissolved in the fluids of the experiment. Thus in a solution 

 of iodide of potassium, with eosin added and exposed to light, 

 iodine is set free ; this does not occur if the solution is freed 

 from oxygen. It has been thought that this oxidizing action is 

 due not to oxygen but to ozone (O 8 ). 



Physiology of Protozoa. It must not be thought that 

 all the protozoa because they are unicellular are primitive 

 creatures and rudimentary ancestors of higher animals ; their 

 cell is adapted to all the requirements of life and possesses, at 

 least in some degree, all the properties of higher animals ; 

 it may be more independent, and richer than certain cells 

 of vertebrates. Both by structure and by function the protozoa 

 are complex and highly differentiated creatures. 



Ehrenberg, an old scientist, who studied them very carefully, 

 held this belief, but in a naive and inaccurate form. Protozoa 

 to him were animals possessing in brief all the organs of 

 higher animals ; he saw in them a digestive tube, a brain, eyes, 

 kidneys, a heart, an ovary and vessels. But nothing of that 

 really exists ; the protozoa have simply nuclei, vacuoles which 

 digest the food, others which expel the waste products and a 

 protoplasm full of varied movements and currents. But 

 although they do not possess the miniature organs which roused 

 Ehrenberg's admiration, they are none the less capable of 

 taking up food, digesting it, and expelling the waste, of moving, 

 and of reproducing. They possess all the functions of animal 

 life, but more simply and more purely than among the higher 

 animals ; what one might call the chemical and physical model 

 of life is in them more visible, more exposed to the eye. 

 That is why their study is so attractive and so fertile ; it is to 

 it we owe our best knowledge and our best ideas on life in 

 general, so there is no necessity for the surprise expressed 

 by those who have only read their family " Buffon " (Buffon's 

 Natural History), that scientists should be passionately 



