550 EXPERIMENT STATION RECORD. [Vol. 40 



appears to be due to paralysis. Miscible oils are practically Instantaneous 

 in their killing action against the living aphids. The action is probably of a 

 chemical nature." 



A list of 11 references to the literature is included. 



The present conditions of lac cultivation in the plains of India, G. 3. 

 Misea (Affr. Jour. India, IS (1918), No. 3, pp. 405-415, pi. 1). — A discussion of 

 the present status of the lac (Coccus lacca) Industry. 



Trench fever. — A report of clinical observations and research as to the 

 etiology, pathology, prophylaxis, and treatment of trench fever among 

 troops, W. Byam et al. (Jour. Amer. Med. Assoc, 11 (1918), Xon. 1, pp. 21-:.,; 

 2, pp. 110-113; 3, pp. 188-193). — This is a detailed report of investigations of 

 trench fever at Hainpstead, England, in which the clothes or body louse was 

 shown to be the active agent In its transmission. A summary of the evidence 

 obtained from the experimental work Is as follows : 



" The whole blood from febrile trench fever cases, up to the fifty-first day of 

 disease, when injected Intravenously, is capable of reproducing the disease. 

 The incubation period in such Infections varies greatly — from 5 to 20 days. The 

 virus as contained In the circulating blood is destroyed by the addition of dis- 

 tilled water In large quantities. 



"The bites alone of Infective lice do not produce trench fever. The excreta 

 of Infective lice when applied to a broken surface of skin do readily produce 

 trench fever. The incubation period of such infections Is remarkably constant, 

 and averages 8 days. The excreta passed b\ lice una fed on trench fever pa- 

 tients are not infective till the expiration of not leas than 7 days from the com- 

 mencement of the feeding on trench fever blood, thus indicating a developmental 

 cycle in the louse or a period during which the organism multiplies 



" Once lice are infective, the] remain so till at least the twenty-third day from 

 the date of their Infection. The virus of trench fever as contained in infected 

 louse excreta is capable of withstanding drying at room temperature, exposure 

 to sunlight, keeping for DOt less than 16 days, and heating to ."id C. [132.S° F.] 

 for 20 minutes. A temperature of 80° for 10 minutes destroys the virus, which 

 is therefore not a spore bearing organism. The bodies Of Infected lie when 

 crushed on the broken skin are capable of producing trench (ever. When lice 

 become so infective remains to be determined. 



"Active trench fever blond equivalent to the content of 11 lice does not pro- 

 duce trench fever when rubbed into the broken skin. Infection probaly does 

 not take place by the mouth or by inhalation. The excreta of lice are not nor- 

 mally capable of producing trench fever. Trench fever Infected lice do not 

 transmit the disease to their offspring. Some attacks of trench fever may be 

 afebrile throughout. 



"The percentage of individuals naturally immune to trench fever is exceed- 

 ingly small. Old age is no bar to Infection. Such Immunity as results from an 

 attack of trench fever is not permanent, and may persist only for so long as the 

 individual shows evidence of the disease. Even as late a< the seventy-ninth day 

 of disease a patient's blood may remain infective and be capable of infecting 

 lice fed on such a patient while febrile. The different varieties of trench fever 

 result from differences in the persons infected .rather than in the source of in- 

 fection." 



The transmission of relapsing fever by the body louse, J. Koch (/»< nl. 

 Med. WehtUChr., 1,8 (1911), p. 1066; abs. in Rev. Bad., 8 [1918), No. 5, p. 85).— 

 During the course of investigations of the transmission of the spirochete of re 

 current fever by Pediculus vestimend the author found spirochetes in the lice 

 from 10 individuals, or in 26 per cent of those examined. The large dumber of 



