March, 1938] Agricultural Research in N. H. 35 



Physiology of the Adult Rumiiiant" (about 200 pages). {Purnell and 

 Adams Funds) 



Sheep Breeding 



In our investigations in sheep breeding, selection for the establish- 

 ment of four functional nipples with a corresponding increase in milk 

 yield and increase in twinning rate, has been continued by E. G. Ritz- 

 man. Out of 58 ewes bred, 28, or approximately 50 per cent, have four 

 or more functional nipples. 



Since this work was begun, other investigators in research on the 

 endocrine functions have demonstrated that the development of the 

 lobe and of the duct system of the mammary gland is directly caused by 

 ovarian hormones, and that the actual secretion of milk results from 

 hormone stimulus. These discoveries which explain the physiological 

 basis of lactation are in accord with the theoretical heredity pattern 

 proposed in an earlier report (N. H. Station bulletin 53) as a possible 

 basis for eventual development into a prediction chart for the selection 

 of breeding stock. 



Progress in the establishment of the lactating function of these ewes 

 has been rapid and consistent but in increasing the twinning rate has 

 been rather sporadic. While this may be in part due to the fact that 

 limitation in the size of the breeding flock has prohibited discarding 

 single-born females, it nevertheless suggests that there is no specific 

 causative relationship between these two typically sexual functions, i. e., 

 fecundity and lactation. 



While it must be generally recognized that increase in fecundity 

 rests primarily on a hereditary basis, yet it is becoming more evident 

 that proper nutrition has a very material influence in realizing the 

 hereditary potentialities. These studies are being continued. {Adams 

 Fund) 



Contact Insecticides 



In their study of contact insecticides, W. C. O'Kane, L. C. Glover and 

 W. A. Westgate are investigating the rate of penetration of oils through 

 insect integument. The work to date has been largely concerned with 

 establishing a suitable technique for measuring the rate of penetration. 

 This work has presented numerous technical difficulties. After exten- 

 sive experimentation an apparatus has been devised which has the 

 following elements. A large-bore glass tube is fused to a capillary 

 glass tube. The end of the large-bore tube is pressed out into a disc 

 of 9 mm. diameter, having a concave curvature similar to that of a 

 sphere of %" radius. The center of the disc has an opening continuous 

 with the tube. A series of these tubes is held firmly in a specially con- 

 structed metal-and-cork block, with movable sections. 



The experimental insect used in all tests to date is the American 

 cockroach, Periplaneta americana. The pronotum of the cockroach is 

 dissected off and cemented to the glass disc, which has a curvature simi- 

 lar to that of the pronotum. The apparatus is filled to the top of the 

 capillary tube with a mineral oil of low boiling point which is then 

 sealed with cement. Thus the oil can escape only through the pronotum 

 which is cemented to the disc. The rate of fall of the oil in the capil- 



