16 N. H. Agri. Experiment Station [Bui. 296 



ing ewes to the breeding flock, thus eliminating some of the older parent 

 stock. The large proportion of young ewes dropping their first lambs 

 has, however, caused a drop in the percentage of twins for the flock 

 as a whole, as only one of these yearlings dropped twins. 



One of the unanswered common results that has always perplexed 

 sheep breeders is the fact that in some years twinning appears to be 

 much more common than in others without any apparent reason ex- 

 plainable on the basis of present knowledge. From many years of ex- 

 perimentation in studying the metabolism of sheep it has been found 

 that a low level in heat production occurs during November and Dec- 

 ember, or in other words, during the early development of the fetus; 

 and it seems quite possible that this low twinning rate may be some- 

 how associated with the low metabolic activity which prevails at this 

 time. 



An outcross has been started by mating a four nippled Suffolk ram 

 (from imported stock) to 21 yearling ewes all of which are four nip- 

 pled. The result will no doubt increase the size somewhat without 

 retarding the four-nippled trait, and it is expected to improve the twin- 

 ning tendency. 



One of the most gratifying results of this work has been the constant 

 improvement in the character of the wool, particularly in its adapt- 

 ability to market requirements. As judged by expert market graders 

 this wool has the strength and length of % blood staple with the tone 

 and spinning qualities of !/•> blood, which places it well at the top of 

 fleece wool. (Adams Fund) 



Contact Insecticides 



Investigations of criteria for laboratory appraisal of wetting and 

 spreading performance of spray materials have been completed and 

 prepared for publication by W. C. O'Kane, J. G. Conklin, L. C. Glover 

 and W. A. Westgate. The criteria studied are seven in number as 

 follows : 



(1) The exposure period as defined in a previous report; (2) time 

 required for individual droplets of a spray to coalesce and wet a sur- 

 face; (3) angle of contact liquid-solid; (4) adhesion tension; (5) sur- 

 face tension of liquid; (6) spreading coefficient; (7) area of spread. 



In general, the materials studied arrange themselves in the same 

 order when appraised by these various criteria. There are some excep- 

 tions, however. For example, angle of contact may give erroneous 

 results unless angles are read at successive time intervals, in order to 

 disclose the behaviour of a droplet upon standing. 



Studies of effects of spray pressure disclose this to be an important 

 factor in the performance of a spray material. 



Investigations have been continued on the penetration of arsenic 

 into insects, and resulting distribution of the poison in various struc- 

 tures and organs. Results of some recent studies were published in 

 June, 1936, in Technical Bulletin 65, "Further Determinations of the 

 Penetration of Arsenic into Insects." This is No. XI in "Studies of 

 Contact Insecticides." {Purnell Fund) 



