60 



tar, and increasing the amount of soap by one-sixth (28 lb.). In 

 Trinidad the sokition is apphed as a spray. The entire mixture should 

 be stirred before each apphcation. The animal after treatment should 

 not be unduly exposed to the hot sun, or driven any considerable 

 distance. Young calves with heavy coats should be bathed with soap 

 and water three or four days after treatment, so as to prevent severe 

 irritation of the skin. In locahties where ticks are numerous it will 

 be found necessary at first to administer the mixture every fifteen 

 days and to exclude the herd, as much as possible, for a definite period 

 from infected areas. 



Bacot (A. W.) & Martin (C. J.). Observations on the Mechanism of 

 the Transmission of Plague by Fleas. — Jl. Hygiene, Cambridge, 

 Plague Supplement III, 14th Jan. 1914, pp. 423-439, 4 figs., 3 pis. 



The conclusion that fleas play an important rdle in the spread of 

 plague was arrived at on epidemiological grounds as long ago as 1897 

 by Ogata. Since that time much work has been done on the trans- 

 mission of plague by fleas. The Commission for the Investigation of 

 Plague in India (1907) discussed the following possible methods by 

 which the flea may transmit plague : (1) by the animals eating the 

 infected fleas ; (2) by the proboscis of the flea mechanically conveying 

 the bacilli from the infected to the healthy animal ; (3) by the salivary 

 glands of the flea becoming infected, the bacilli being then inoculated 

 along with the saliva ; (4) by a regurgitation of the stomach contents 

 through the oesophagus and pharynx, the bacilli being then injected 

 with the saliva, or on the pricker, or being rubbed into the wounds 

 made by the pricker ; (5) by a retention of infected blood in the 

 pharynx or about the mouth parts of the flea, the bacilli multiplying 

 there and then being inoculated into the animal as in (4) ; (6) by the 

 bacilli contained in the faeces being deposited on the skin, and then 

 being either injected by the pricker or rubbed into the wounds made by 

 the pricker. Methods 1 to 3 are set aside on what seem satisfactory 

 grounds. Many hundreds of fleas were dissected, but in no case were 

 plague bacilh found outside the alimentary canal and the authors 

 state that their observations agree on this point with those of the Com- 

 mission. Experiments on (6) carried out by the Commission and by the 

 authors demonstrate that transmission of the plague by this method 

 is possible. The authors applied to bitten areas on rats, (a) the 

 surface of the spleen of a rat recently dead from plague ; (6) a strong 

 emulsion of plague bacilli from the stomachs of fleas, which had been 

 nourished on animals with septicaemia. In both cases some of the 

 rats died of the plague. One difference between the bacilli from the 

 spleen and those from the flea's stomach was that the former were not 

 taken up by the phagocytes of the authors' own blood whereas the 

 latter were ingested freely. Other observations led to the beUef 

 that bacilli grown in the stomach of the insect are not of a high degree 

 of virulence. Infection by this means must leave much to chance. 

 Experiments were then made to ascertain whether or not the flea 

 could infect during the act of sucking. Details of these experiments 

 are given and in all the possibility of infection by dejecta was pre- 

 cluded. Under these conditions it was found that two species of rat- 

 fleas, Xenopsylla cheopsis and Ceratopkylhis fascial >is, fed upon septi- 



