194 G. G. Heslop: 



tion has been induced solely by the fact that the animal is affected 

 with contagious pleuro-pneumonia. In one of the eases quoted 

 a positive complement fixation result was obtained, but no lesions 

 of the disease could be discovered in the lungs when the animal 

 supplying the test serum was subsequently submitted to a post- 

 mortem examination. That the reaction might be a group reaction 

 for filterable viruses in general, and not absolutely specific for the 

 filterable virus causing contagious pleuro-pneumonia in cattle 

 seemed possible. Of the diseases in cattle due to filterable 

 viruses, only two, e.g., contagious pleuro-pneumonia and cow 

 pox (Variola) are present in Australia, so that tests for com- 

 parative purposes have of necessity been confined to tests of 

 sera from animals known to be affected with cow pox. 



Samples of sera taken from a cow at the Veterinary School 

 which was affected with extensive cow pox vesicles and pustules 

 on the mammary gland, were tested and were found to give 

 positive complement fixation results with the contagious pleuro- 

 pneumonia antigen. The possibility of the same animal being 

 affected with contagious pleuro-pneumonia as well as with cow 

 pox was negatived by the general appearance of the animal and 

 her previous history. 



Through the courtesy of Dr. W. J. Penfold, Director of the 

 Commonwealth Serum Laboratories, I have been able to obtain 

 serum samples from 11 calves, which had been vaccinated with 

 the virus of cow pox in the manufacture of vaccine lymph for 

 human vaccination. Each of the calves had given a typical re^ 

 action to the vaccination. 



On submitting the samples to complement fixation tests with 

 the contagious pleuro-pneumonia antigen, it has been found 

 that they all show some ability to inhibit haemolysis. 



It is apparent therefore, that in carrying out tests with sera 

 from an unknown source, the serum of an animal affected only 

 with cow pox may cause sufficient inhibition of haemolysis in 

 a complement fixation test for contagious pleuro-pneumonia to 

 give rise to the assumption on the part of the person carrying out 

 the test that the animal supplying the test serum is affected with 

 contagious pleuro-pneumonia. 



Serum from the cow affected with cow pox at the Veterinary 

 School, which serum gave a positive complement fixation reaction, 

 and the three samples of calf serum, which showed the greatest 

 amount of inhibition of haemolysis in the complement fixation 



