840 THE FILTRABLE VIRUSES 



the filtrate when it is kept at 20 C., but will not grow in ordinary broth. The filtrate 

 as the result of the multiplication of these organisms becomes slightly opalescent. 

 Under similar conditions, the filtrate occasionally contains certain structures which 

 Borrel regards as belonging to the Protozoa and to which he has given the name 

 Micromonas mesnili. 



With the object of protecting sheep against sheep-pox the animals are 

 immunized by infecting them with a mild form of the disease. Vaccination 

 [or clavelization] is effected by inoculating a small quantity of lymph from 

 the pustules with a lancet on the tail or on the internal surface of the ear. 



The inoculation is not without danger : some of the animals die (1-10 per 

 cent.). Borrel hyper-immunized sheep which had recovered from sheep- 

 pox by inoculating them on several occasions with lymph from the inoculation 

 pustule, and obtained a serum which had prophylactic and therapeutic 

 properties : the inoculation of 10-20 c.c. of this serum has arrested the 

 mortality in flocks exposed to infection. 



"Infectious epithelioses." 



Borrel has introduced the term " infectious epithelioses " to denote a number of 

 diseases having a special affinity for the epithelial tissues and caused by " filter- 

 passing organisms " : sheep-pox, cow-pox, foot and mouth disease, rinderpest, 

 epithelioma contagiosum of fowls and molluscum contagiosum. In sheep-pox there is 

 always present a characteristic and specific element, the sheep-pox cell, having a 

 vacuolated nucleus with pseudo-parasitic inclusions (due probably to the penetra- 

 tion of poly-morpho-nuclear cells which in these cells undergo a process of degenera- 

 tion) . wherever the virus settles it produces a proliferation of the epithelial tissues, 

 and (in the liver, kidney and lung) epithelial growths which develop at the expense 

 of the pre-existing cells of the part. There can be no doubt but that these changes 

 bear a considerable resemblance to the evolution of cancer growths, so that the 

 hypothesis might be put forward that the cancer virus enters into the category of 

 filter-passing organisms. This is merely an hypothesis, and it must be noted, as 

 Borrel says, that the metastases of sheep- pox are absolutely different from cancer 

 metastases : for example, the metastases in the lung in the former case represent a 

 proliferation of pre-existing cells, while cancer metastases are produced by a graft 

 in the lung of cancer cells from the original tumour. 



SECTION VII. THE VIRUS OF COW POX. 



[Variola vaccinia.] 



If the fresh exudate from the vesicles of an heifer suffering from cow pox 

 be rubbed up with 10-12 times its weight of water and filtered through a 

 Berkefeld V bougie a filtrate is obtained which according to many investigators 

 has proved to be infective. 



The virulence is only manifested if before filtration the lymph is left to 

 macerate for a long time in sterile water (Carini } Negri). The first emulsion 

 of lymph is left in the ice chest for 2 or 3 days then rubbed up and replaced 

 in the ice chest for a fortnight. It is not until now that the product is filtered, 

 first through wool then through paper and finally through a Berkefeld bougie. 



Negri soaked up the filtrate on a small piece of sterile absorbent wool and placed 

 it on the cornea of a rabbit (which had been previously scarified) for about 10 hours. 

 A typical pustule developed the contents of which were infective and produced 

 similar effects on the cornese of other rabbits in series, and on the skin of a calf. 

 With a similar filtrate Remlinger and Osman Nouri have been able to produce a 

 typical vaccinal eruption on the shaved skin of guinea-pigs and rabbits. 



In these investigations, the inoculations should be performed on a number of 

 animals : for the virus is partially retained by the bougie, and the filtrate is conse- 

 quently not highly infective (p. 836). 



The filtrate inoculated beneath the skin of a susceptible animal immunizes 



