ANIMAL MECHANICS. 



151 



a few days' instruction, the sac of the hydrocele was emptied 

 and injected with two drachms of tincture of iodine. The pa- 

 tient then urinated at intervals of one minute into the test 

 tubes previously prepared, commencing at one minute after 

 the injection. The fourth test tube responded faintly to the 

 starch test for iodine ; and the fifth and subsequent tubes 

 showed its presence very distinctly. From this experiment 

 it is evident that the entire process, viz., absorption by the 

 tunica vaginalis ; transmission by the lymphatics and capillary 

 veins to the heart ; retransmission by the renal arteries to the 

 kidneys ; secretion of urine, and its transmission to the bladder 

 by the ureters — occupied less than four minutes ; or about 

 five times the entire time required for the circulation of the 

 blood. 



8. On the Muscular Forces employed in Parturition. — 



In the first stage of natural labour, the involuntary muscles of 

 the uterus contract upon the fluid contents of this organ, and 

 possess sufficient force to dilate the mouth of the womb, and 

 generally to rupture the membranes. I shall endeavour to 

 show, from the principles of muscular action already laid down, 

 that the uterine muscles are sufficient, and not much more 

 than sufficient to complete the first stage of labour, and that 

 they do not possess an amount of force adequate to rupture, 

 in any case, the uterine wall itself. In the second stage of 

 labour, the irritation of the foetal head upon the wall of the 

 vagina provokes the reflex action of the voluntary abdominal 

 muscles, which aid powerfully the uterine muscles to complete 

 the second stage, by expelling the foetus. The amount of 

 available additional force given out by the abdominal muscles 

 admits of calculation, and will be found much greater than the 

 force produced by the involuntary contractions of the womb 

 itself. 



The mechanical problem to be solved for both cases is one 



