134 THE EFFECTS OF PARASITES ON THEIR HOSTS. 



crowd themselves into so short a space of time that it is difficult to 

 determine the effects of the individual factors. After a. more copious 

 infection in the case of pigs and rabbits, a more or less conspicuous 

 reddening of the peritoneal covering of the intestine and the ab- 

 dominal walls may often be observed within the second week, and 

 sometimes even a matting together of the viscera, or a serous effusion 

 into the body-cavity. All these phenomena, although not hitherto 

 observed in man, can only be produced by embryonic wanderings. 

 Virchow is of opinion that the typhoid conditions which accompany 

 trichinosis may also be explained as the direct consequences of the 

 wandering, but perhaps it would be nearer the truth to refer them to 

 the absorption of the waste products, which are produced in masses by 

 the destruction of the muscular tissue. It appears to me very doubt- 

 ful whether the Trichina-embryos have any influence, as is supposed, 1 

 in virtue of certain inherent chemical properties. 



Filaria Medinensis has also sometimes been accredited with 

 poisonous properties, in order to explain the dangerous results which 

 follow the tearing out of the worm ; but it has been shown by the 

 researches of Bottcher 2 that these symptoms are caused merely by 

 the wandering of the embryos in countless numbers into the sur- 

 rounding tissues, and that they are mainly of an inflammatory nature. 



Similarly the embryos of Stronyylus filaria hatched in the lungs 

 of sheep and other ruminants frequently occasion a more or less ex- 

 tensive inflammation, which only ends favourably if the parasite 

 obtain an exit. Very different from such general inflammations are 

 the changes caused by the invasion of the embryos of Ollulanus* 

 which occur in the neighbourhood of each individual worm, and again 

 present all the appearances of a miliary tuberculosis, and are no less 

 dangerous than the Cestodic tuberculosis just mentioned. 



Further, it is not so much the wanderings that act as causes of 

 disease, as the irritations and injuries produced by them. This is most 

 strikingly proved by the history of the so-called Filaria sanyuinis (p. 

 50), which sometimes circulates in millions in the blood of its host, 

 yet only causes disturbances when it gives rise to haemorrhage in 

 making its exit into the cellular tissue, or through the kidney, where 

 it perforates the capillary tuft of the Malpighian body. The haema- 

 turia or chyluria which is caused in this way, and also that resulting 

 from the operations of Distomum, if of long continuance, are followed 

 by anoemic conditions, but this is generally the only expression of the 

 helminthiasis. 



1 Friedreich, Deutsckes Arckiv f. klin. Med., p. 265, 1872. Huber is of the same 

 opinion in regard to Ascaris lumbricoides, Ibid. p. 450, 1870. 

 8 Sitzunysb. der Dorpater NuturforscJiergesellsch., p. 275, 1871. 

 ' See Bugnion and Stirling at the places mentioned on p. 47. 



