Studies upon plague in ground squirrels (in four parts) ... : II. A plague-like disease of rodents / by George W. McCoy.

  • McCoy, George W.
Date:
1911
Catalogue details

Licence: Public Domain Mark

Credit: Studies upon plague in ground squirrels (in four parts) ... : II. A plague-like disease of rodents / by George W. McCoy. Source: Wellcome Collection.

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    to report any experiments tending to show that an organism was so small as to pass through one of these filters, and consequently small enough to raise a question as to whether it might belong to the class known as ultra-microscopic organisms. However, every experi- ment showed that the causative agent did not pass through the Berkefeld filter. In each case control animals died of the disease in the usual time, while those inoculated with the filtrate, secured under a negative pressure of 15 pounds, remained well. MODE OF TRANSMISSION. Several experiments have been made for the purpose of learning the natural mode of transmission of the disease. CONTACT, On several occasions healthy guinea pigs and ground squirrels have been put in small cages with infected rodents, left there until the latter died and kept in the uncleaned cage for several days after the death of the sick one, but in no-case was the disease transmitted even under these circumstances of intimate contact. It has been shown that feeding experiments are successful in transmitting the disease. We have good reason for believing that in nature it is not ordinarily transmitted in this manner. The reason for this is the fact that in the feeding experiments the buboes of the animals infected by ingestion were in the neck or in the mesentery, while when the disease is naturally contracted by squirrels the bubo is often situated in other parts of the body, axilla, pelvis, or inguinal regions. As the most prominent feature of the disease in most naturally infected rodents is a lesion of the peripheral lymph glands, it would seem reasonable to believe that the infection usually gains entrance through the skin. The unsuccessful contact experiments, four in number, in which healthy guinea pigs were kept with sick ones and allowed to remain in the cages, some of which were very filthy by reason of the accumulation of urine and feces from the sick and the well animals, negatived the probability that the disease was transmitted by means of contact with sick animals or their excretions. INSECT TRANSMISSION. It is more in keeping with our present views of the transmission of many infectious diseases to look for a living carrier, and as this disease has so many points of resemblance to plague, which has been shown to be readily transmitted among rats, guinea pigs, and squir- rels by means of fleas, we naturally turned to these parasites as a probable means of conveying the disease. It was found possible to reproduce the infection in guinea pigs by subcutaneous inoculation with crushed squirrel fleas (Ceratophyllus acutus) taken from a squirrel or from a guinea pig dead of the disease. The successful
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