368 MR T. ARTHUR HELME ON HISTOLOGICAL OBSERVATIONS ON 



Now these facts must have a relation to the rapidly approaching completion of the 

 uterine function, i.e., parturition. 



It seems as if each cell of the uterus had its life-history distinctly laid down for it, 

 and involved within itself. In the virgin state the fibres are in an undeveloped state ; 

 their power of development is latent, to be called out on the application of some stimulus, 

 e.g. , conception. When this occurs, each fibre develops to its utmost, and during its evolution 

 brings about the reason for its own involution. The augmentation of the volume of each 

 individual fibre is seen to occur with greater rapidity the nearer one gets to the end of 

 pregnancy, until at the full term the enlargement is so rapid that the supporting frame- 

 work which conveys the nutriment has no time to accommodate itself to the rapidly 

 increasing pressure of the distending muscle cells. Consequently, the nourishment begins 

 to be cut off, and at the same time a second and a third factor are at work in the same 

 direction, viz., the diminution of the lumen of the vessels by a similar process occurring in 

 their muscle coat and lining endothelium, and the rapid development of plasmodia 

 (assisting in compressing the smaller vessels). 



As a result of their interference with its blood supply, the muscle cell becomes more 

 and more irritable, so that the contractions of the uterus, which are normally occurring, 

 become increased in intensity. This is well known to occur in the human female, the 

 increased frequency and intensity of the uterine contractions being looked upon as one 

 of the signs of approaching labour. One of the most powerful stimuli for induction of 

 muscular contractions of the uterus (as I have found during the course of experiments 

 with the artificial circulation of the uteri of sheep) is a momentary stoppage of the 

 blood-stream. While the blood-stream is flowing, the normal contractions of the uterus 

 go on rhythmically, but almost coincidently with the stoppage of the stream a violent 

 contraction of much greater intensity and much increased duration occurs. Now it 

 seems to me that as the result of the interference with the blood-stream, as I have 

 described in the pregnant uterus, the muscle cells become more and more irritable and 

 respond more and more intensely to any stimuli. The result of this increased irritability 

 of the uterine muscle is the intensification of the uterine contractions, which find their 

 culminating point in the act of labour. 



But in the evolution of the uterus, not only have the needs of labour been provided 

 for, but also those of the puerperium. 



And here I should wish to draw attention to the sinus-like character of the thin- 

 walled veins, in relation to the risk of haemorrhage. This is perhaps more important 

 in the human being, where the risk is greater. In this sinus-like character of the veins 

 we see a beautiful natural means for the arrest or prevention of haemorrhage. As the 

 foetus is expelled, and the placenta detached, the uterine musculature contracts, and at the 

 same time retracts, so that the extent of the uterine surface remains permanently smaller. 

 The result of this retraction is a readjustment of or alteration in the planes of the con- 

 nective tissue, and a consequent compression and blocking of the uterine sinus-like veins. 

 If I may allude to the human uterus again, this is no doubt the explanation of the arrest 



