Etiology. 439 



time, it may slip into the section situatefl immediately behind 

 it. In consequence of the contraction of the circular muscle 

 fibers, in peristalsis progressing towards the anus, a piece of in- 

 testine becomes thinner and longer, the next posterior piece, 

 however, becomes wider and shorter in consequence of contrac- 

 tions of the longitudinal muscle fibers; the thinner and longer 

 section can easily slip into the wider and shorter piece, if this 

 becomes more or less fixed, or less motile, or if the section 

 nearer to the stomach meets with an impediment at its proximal 

 end. Nothnagel has shown by animal experiments that such 

 invaginations may occur in normal peristalsis, that they are, 

 however, at once replaced, because only short portions are in- 

 vaginated and the contractions do not last long. Permanent 

 invagination occurs only in abnormally active and energetic 

 peristalsis. Hence all stimuli which increase peristalsis may 

 bring about invagination indirectly. 



The peristalsis may be increased in all or in certain parts 

 of the intestines, and become convulsive in sections, after a cold, 

 after the ingestion of ice cold water or cold feed (frosted grass, 

 frozen bulbs), in the course of an intestinal catarrh or enteritis, 

 in the presence of intestinal parasites, foreign bodies, tumors 

 of the intestinal wall, and in attacks of intestinal colic. These 

 conditions, in combination with predisposing causes to be men- 

 tioned presently, may bring about invagination. (Wagenheuser 

 has seen seven cases occurring at the same time in foals after 

 the ingestion of frosted grass.) 



In agonal states the increased amount of carbon-dioxide of 

 the blood which causes increased peristalsis not infrequently 

 produces invagination; this, however, occurs so late that no 

 more circulatory disturbances can develop in the invaginated 

 portion of the intestine (agonal invagination). 



It is not impossible that in certain cases a section of intes- 

 tines, which is just contracting, may become invaginated into a 

 neighboring piece by a sudden great increase of intraabdominal 

 pressure. This may explain those cases in which horses sud- 

 denly fall sick in jumping, and cattle in running about, or during 

 parturition, or in drawing a load uphill. Even in these cases, 

 however, the peristalsis which has become more intense, is prol)- 

 ably the immediate causative factor. 



Both veterinary and medical authors still claim frequently that invagination is 

 brought about on certain occasions in such a manner that sections of intestines sit- 

 uated towards the anus Ijecome paralyzed and that sections situated toward the 

 stomach, wliich are quite motile, slip into the paralyzed portion. In this manner 

 sections are paralysed during the agonal stage and other sections are still very 

 motile. The authors cannot indorse this socalled paralytic theory. If it were true 

 then invagination should be equally frequent in all species of animals, and young ani- 

 mals, in whom even insignificant stimuli are liable to excite lively peristalsis, should 

 not be affected preferably. One would not expect the great rarity of the affection 

 in horses which offer so many chances to partial intestinal paralysis (thrombosis 

 of the mesenteric vessels). It would also not be obvious why very long sections of 

 the intestines are frequently invaginated. Nothnagel could not verify the paralytic 

 theory in his experiments. 



