114 



Journal of Agricultural Research 



Vol. IV. No. 2 



Escherich and Miyajima (4) in their work on Wipfelkrankheit con- 

 sider the blood of nun-moth caterpillars as an absolute and reliable index 

 of conditions existing within the tissue nuclei. Before using caterpillars 

 for their experiments, these authors repeatedly examined the blood for 

 polyhedra, allowing a stated interval to elapse between successive exam- 

 inations. If the last test did not reveal polyhedra within the corpuscles, 

 the caterpillars were diagnosed as healthy; if the blood contained poly- 

 hedra, however, the animals were pronounced diseased and were dis- 

 carded. Such a procedure consumes a great deal of time, and since time 

 is an important factor in a working season that extends over only eight 

 weeks this method was soon abandoned by the writer in his experiments 

 on gipsy-moth caterpillars. In order to procure healthy material, a 

 much more serviceable method, described in the section dealing with the 

 infection experiments, was used. Nevertheless, in order to ascertain 

 the accuracy of the blood test, the haemolymph of a large series of cater- 

 pillars was examined, after which they were sectioned, that conditions 

 within the tissue nuclei might be checked with the appearance in the blood. 

 Table I gives the results of one series of experiments. 



Table I. — Results of blood tests and tissue examination of gipsy-vwth caterpillars^' 



o The words, "few," "moderate," and "large" in Table I are simply comparative terms that are also used 

 by Escherich and Miyajima (4). A "few polyhedra within the corpuscles" means an occasional find, 

 possibly one or two scattered over many fields examined. By " moderate number " is meant two or three 

 polyhedra within perhaps a third of the corpuscles in a field and represents also a few out in the plasma. 

 Blood classified under " large number " gives a good picture of a caterpillar in the last stages of the disease, 

 for nearly every corpuscle is beset with numerous polyhedra, and, likewise, many are floating about in the 

 plasma. 



