ZOOLOGY AND BOTANY, MIOROSOOPY, ETC. 267 



j3. ScMzomycetes. 



Doctrine of Phagocytes.* — The interest excited hy the ingenious 

 hypothesis of Metschnikoff is shown by the number of experiments made 

 and articles written in support or contradiction of the assumption that 

 the mesoblastic cells of Vertebrata inherit the capacity of absorbing and 

 destroying pathogenic bacteria from their ancestors, the unicellular 

 amoebae, the mesodermic cells of Coelenterata, Turbellaria, &c. Dr. H. 

 Bitter, in his critique on the doctrine of phagocytes, thus balances the 

 evidence for and against the theory. 



Unicellular lower animals, amoebae, and also mesodermic cells of 

 sponges, take up small plants into their protoplasm, and digest them. 

 In more highly organized animals this intracellular digestion becomes 

 extracellular and fermentative ; certain cells, however, still possess a 

 capacity for picking up and dissolving foreign bodies. This contrivance 

 is regarded by Metschnikoff as a special arrangement whereby harmful 

 elements, especially pathogenic micro-organisms, are prevented from 

 penetrating the animal economy, the process being complicated by the 

 resistance made by the parasite to digestion. Those cells which are 

 able to digest foreign bodies are called phagocytes, and are further sub- 

 divided into large and small. Infectious diseases are recovered from 

 when the phagocytes overmaster the exciting causes, and immunity after 

 one attack or after inoculation depends on the phagocytes having become 

 accustomed to combat the micro-organisms. 



This theory is supported by Metschnikoff's observations on Daphnise 

 which are attacked by a torula with needlelike ascospores. These latter 

 having been swallowed penetrate the tissues ; as soon as this happens, a 

 leucocyte appears, and the spores are enveloped and destroyed. If the 

 spores remain unattacked and germinate, the animal is infected. In frogs 

 too, anthrax bacilli are taken up by leucocytes, and destroyed. At a 

 temperature of about 30°, only a few leucocytes take up the bacilli, and 

 the animals become infected. This is explained on the hypothesis that 

 the anthrax bacilli are more potent at this temperature owing to their 

 being accustomed to deal with warm-blooded leucocytes. In warm- 

 blooded animals Metschnikoff rarely found bacilli in leucocytes, but if 

 the animal had been protected by a weakened virus, the bacilli were 

 picked up in quantities and destroyed. Hence it is concluded that 

 immunity is derived from the leucocytes having got used to the poison 

 of the bacteria. 



Bacteria-eating phagocytes were also found in erysipelas and 

 relapsing fever, and are also assumed to be present in gonorrhoea, 

 leprosy, and tuberculosis. 



According to Hess, the phagocytic privilege is shared by the cells of 

 the splenic parenchyma, and of the liver, and Eibbert asserts that the 

 spores of various kinds of Aspergillus and Mucor are got rid of in a 

 similar manner. If, however, many spores be injected, the number of 

 leucocytes may not suffice to prevent their development, and this lastr 

 mentioned author also believes that the viability of the fungi is 

 diminished by the leucocytes cutting off the supply of oxygen. Other 

 facts in support of the theory are that if an animal siarvive the intro- 

 duction of a small quantity of spores, there will be found, on a second 

 injection, a much larger number of leucocytes, and that, as stated by 



* Zeitschr. f. Hygiene, iv. (1888) No. 2. 



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