BIOLOGY IN ITS WIDER ASPECTS 128 1 



Ix Illustration : the Conquest of Distemper. — A dramatically 

 clear instance of the biological control of life is the discovery which 

 Messrs. G. W. Dunkin and P. P. Laidlaw have made that dog- 

 distemper can be baulked by a vaccine treatment. The trouble- 

 some and costly disease has been a shadow for many a year; but 

 man seems to have conquered it at last. For a long time it has been 

 recognised that distemper is a microbic disease, somewhat analogous 

 to measles and scarlatina in children. While predominantly catarrhal, 

 affecting the lining of the nasal passage, it may spread to the lungs 

 and the food canal, the liver and the nervous system. It is particu- 

 larly common in puppies between four and eleven months, but 

 increasing age does not give any complete protection. An attack in 

 early life usually confers immunity if the animal survives, but this 

 is by no means absolute. The general treatment in the past has 

 been to administer internal disinfectants and to try to keep up the 

 patient's strength, though by means of very light food. 



One of the reasons why distemper has baffled investigators for 

 so long is that the disease often occurs in conjunction with other 

 microbes besides the specific one. In other words, there may be a 

 mixed infection. The second reason is that the distemper microbe 

 is much smaller than an average bacillus. It belongs to the elusive 

 series of "filter-passers" or filterable viruses, including, for instance, 

 the causes of smallpox, rabies, foot-and-mouth disease, and, accord- 

 ing to some authorities, measles and scarlet fever. There are also 

 many plant diseases that are due to filterable viruses. 



In 1926 Dunkin and Laidlaw showed that a pure form of distemper 

 could be produced in ferrets infected from dogs. It can be transmitted 

 from dog to ferret, from ferret to ferret, from ferret to dog, by 

 material in which no bacteria can be demonstrated. In their further 

 experiments at the Medical Research Council's Farm Laboratories 

 at MiU Hill, the investigators prepared from infected ferrets a 

 vaccine that immunises either ferrets or dogs. A convenient form of 

 the vaccine is a formaldehyde extract of the infected ferret's spleen; 

 and a large dose of this non-living vaccine will induce immunity 

 in about 90 per cent, of the ferrets into which it is injected. But to 

 consolidate the immunity thus induced, it is necessary to administer 

 living virus. It is probable that what is brought about in the dog or 

 the ferret is some general change in the cells of the body, and not 

 the production of some specific anti-body or counteractive in the 

 blood. The triumph is that dogs may be rendered immune to a 

 common and vexatious disease, and that a single dose may be enough. 

 A dog first treated with the formalised extract from the tissue of 

 a distemper dog, and subsequently with living virus, appears to 

 have acquired solid long-lasting immunity, firm against other strains 

 of dog-distemper. The investigators deserve the heartiest congratula- 

 tion. The next step is the large-scale production of the immunising 



VOL. II NN 



