2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 93 



D. C, for wave lengths of 3130 A to the solar limit at 2970 A, From 

 their data there have been computed an average value of 55 microwatts 

 per cm' (550 ergs/sec. cm'') for the above-mentioned wave lengths in 

 July sunlight between 9 : 00 a. m. and 3 : 00 p. m. at Washington, D. C. 

 This value has been used in translating into terms of days the exposures 

 employed in some of the tests reported here. 



The ova of Toxocara canis are globular, subglobular, or slightly 

 ovoid in shape and of a light brown color. Externally, the egg is 

 covered with a thick, albuminous coating which is mammillated at 

 regular intervals. The eggs var}^ in measurement from d>2 to 102 jx 

 in length and 79 to 96 /x in width. The ova of Toxascaris Icon'ma are 

 ellipsoidal to subglobular or globular in shape, with thick, double- 

 contoured, smooth, clear shells. They measure 82 to 96 [x in length and 

 82 to 92 IX in width. 



REVIEW OF LITERATURE 



The effect of ultraviolet irradiation on the ova of Ascaris eqnorum 

 (= A. mcgaloccpJiala) has been studied in some detail by a number of 

 investigators. Most of these experiments were conducted from the 

 standpoint of the cytologist with a view to determining the effect of 

 the light on various parts of the egg or on the whole egg at different 

 stages of development. Stevens (1909), using a total arc exposure, 

 found that exposure of the whole egg to ultraviolet light for 6 to 

 8 hours did not usually kill the egg at once, but prevented further 

 development when the eggs were in the 2- to 4-celI stage at the time of 

 exposure. Exposure for a period too short to prevent further cleavage 

 (■| to 3 hours) caused various irregularities in development including 

 irregular fragmentation of the chromosomes, delay in cleavage and 

 abnormal gastrulation. Stevens believed that ova arrested in develop- 

 ment may be said to be paralyzed to such an extent that they are unable 

 to initiate any further mitosis. 



In his extensive experiments in exposing various parts of the egg of 

 A. cquoruni to ultraviolet light Schleip (1923) employed the micro- 

 scopic method devised by Hertel ( 1904) and modified and improved by 

 Tschachotin ( 1912) . The apparatus used gave a spectral line of 2800 A 

 from the magnesium arc. Schleip found that irradiation of the whole 

 egg or various parts of the egg for varying periods of time resulted in 

 a marked lethal effect. Schleip concluded, moreover, that no part of 

 the egg could be influenced by ultraviolet light without producing 

 secondarily some alteration in other parts not exposed to the light. 



Ruppert (1924) also employed the apparatus of Tschachotin in 

 irradiating the ova of A. equorum. In Ruppert's experiments short 



