1 36 Lectures on Bacteria. [^ xii. 



bodies of similar structure, they are subject during their life to 

 constant changes of shape in their soft viscid substance, ex- 

 hibiting undulatory movements of their outline and alternate 

 protrusion and retraction of processes (see Fig. 19). These 

 amoeboid movements, as they are called, are combined with the 

 power of taking up and absorbing solid bodies, or oil-drops, or 

 similar objects into their soft substance. If the foreign body 

 comes into contact with the surface of the amoeboid cell, the 

 latter puts out processes which embrace it, and gradually close 

 over it as the waves close over a drowning animal, so that it 

 lies at last inside the soft cell-substance. It may be cast out 

 again at some future time, but it may also sufier decomposition 

 inside the cell, be killed, and disappear. 



In connection with these well-known facts, and also with the 

 observation made by him in the case of a disease in some small 

 crustaceans caused by the invasion of a peculiar Sprouting 

 Fungus, that the cells of the Fungus were absorbed by the colour- 

 less blood-cells of the animal and decomposed in it, that there 

 was a struggle, so to say, between the parasitic Fungus and 

 the amoeboid cells of the animal, Metschnikoff investigated 

 the behaviour of the colourless blood-cells of the vertebrate 

 animals to the Bacillus of anthrax. He found that the virulent 

 rods when introduced by inoculation into an animal liable to 

 take the fever, such as a rodent, were absorbed by the blood- 

 cells only in exceptional instances. They were readily absorbed 

 by the blood-cells of animals not liable to the disease, as frogs 

 and lizards, when the temperature was not artificially raised 

 (Fig. 1 9), and then disappeared inside the cells. The same thing 

 happened when susceptible animals were inoculated with Bacillus 

 Anthracis which had been attenuated to the harmless state. 

 Chauveau had already stated that the attenuated Bacilli pass into 

 the lungs and liver of the animal and there disappear. From all 

 these data we must assume with Metschnikoff that the Bacillus is 

 harmless because it is absorbed and destroyed by the blood-cells, 

 and injurious because this does not happen; or at least that it 



