124 THE UNIVERSITY SCIENCE BULLETIN. 



This problem, then, was deemed worthy of investigation, and for 

 'study the foetal pig was chosen, largely because it shows the typical 

 mammalian characteristics and because little work of any sort has 

 been attempted with the foetal pig; then, too, the material was fairly 

 easily obtained and was found to be highly satisfactory. Since the 

 pig had been selected, a further phase of the subject arose, and its 

 importance became evident: as yet (as we believed after a search 

 through literature) no one had studied the thymus in any great 

 number of foetal pigs and had tabulated measurements and thus 

 secured normal averages and percentages. Such tables of averages, 

 etc., we recognized to be of great value as a basis for further work 

 in this direction or in any phase of thymus work in pigs. Ex- 

 tensive work of this sort has been done by Hatai (5) and by 

 Jackson (6) in albino rats, and by others. 



Therefore, it is with this twofold purpose that this paper is pre- 

 sented: (1) to give our findings as to the relation of the size of the 

 thymus gland to the size of the foetal pig, and (2) to furnish, as a 

 possible basis for further research, tables of measurements and 

 weights of many individual pig foeti of various sizes, with the meas- 

 urements and weights of their thymi and individual and group aver- 

 ages. We hope to further continue the study to include postnatal 

 pigs; in this study a further object of interest will be the determi- 

 nation of the time of the involution stage, since such time would be 

 expected to lie in the postnatal period. 



METHODS OF OBTAINING SPECIMENS AND LABORATORY 

 TECHNIQUE USED. 



Specimens were obtained from the plant of the Armour Packing 

 Company in Kansas City, Kan. The collectors went on the killing 

 floor of the plant, secured suitable uteri, removed the foeti, tied the 

 umbilical cords, and put the pigs into a preservative solution (for- 

 maldehyde) ready for shipping. Litters were kept separate by 

 means of cheesecloth bags for individual litters. Care was taken 

 to get foeti of as wide a range of lengths as possible, varying from 

 9.5 to 28.5 centimeters. 



In the laboratory each pig was weighed, its length recorded (head 

 to rump measurement taken), and its sex determined; then each 

 pig was given a litter letter and a serial number, and tagged so that 

 future identification was possible. The remaining procedure in the 

 actual bulk of the work was simple, and the dissection progressed 

 rather rapidly once the technique was mastered, and an exact idea 

 of the extent of the thymus was secured. The neck and upper 



