No abstract

Six factorial experiments were conducted to examine the effects of thawing solutions consisting of non-electrolyte or of a combination of non-electrolyte and sodium citrate on the survival of ram spermatozoa pellet frozen with a raffinosecitrate diluent.When only non-electrolyte was present in the thawing solution best performance with fructose was achieved at higher tonicity than with inositol, glucose, lactose, or raffinose. With thawing solutions consisting of two components cell survival improved with a decrease in sodium citrate and simultaneous increase in non-electrolyte concentration. Inositol and glucose required higher concentration than lactose and fructose.The best and similar survival rates following I : 4 pre-freezing and I : 3 (pellets: thawing solution, v/v) thawing dilution were obtained with 388·5 mM fructose and with inositol or glucose both at 210 mM concentration and each combined with 40 mM sodium citrate.

Summary. To detenniiie whether selective absorption of immunoglobulin occurs in newborn unamiesthetised calves, the concentrations of IgGj, IgG^. IgM and IgA were measured in thoracic duct lymph shortly after the feeding (if colo.strum. In the 13 calvx-s studied it was found that the coiicenlrations of IgC|, IgCj, IgM and IgA in lymph expressed as a proixtrtiun of the concentration of the same immunoglobulins in the colostrimi fed were not siffnificantly different. It i.s concluded that immunoglobiiluis in the niulecular weight range of 150,000 lo 1,000,000 are absorbed non-selectively in the calf.INTRODUCTION.

The factors affecting lipid absorption in unanaesthetized calves less than 24 hr old have been studied by comparing the output of lipid in the thoracic duct lymph of calves fed one of the following diets: (1) colostrum, in which the colostral fat was replaced with milk fat globules; (2) milk; (3) colostral whey containing milk fat globules; (4) isotonic saline containing milk fat globules. The animals were fed after they had recovered sufficiently from the operation to stand and suck from a nipple feeder.In calves fed diets 1 and 2 the maximum output of lipid in lymph occurred 12 and 6 hr after feeding respectively. In contrast, lipid absorption in calves fed the casein-free diets 3 and 4 was rapid, the maximum output of lipid in lymph occurring at 2-3 hr. It is apparent from these results that newborn calves are capable of absorbing large quantities of lipid and that the delayed absorption associated with colostrum and milk feeding was a function of casein concentration.The lipid in all diets was absorbed with equal efficiency. It was evident from a comparison of the rate and efficiency of lipid absorption in calves fed diets 3 and 4 that factors in colostrum known to be associated with enhanced protein absorption do not significantly influence lipid absorption.Immediately prior to feeding, lymph flow had reached comparatively stable values of 536±5·4 ml/hr (mean ± S.E.) for 13 calves. Flow increased almost twofold within the first 2-3 hr after feeding colostrum and remained elevated for a further 3-4 hr. This occurred in the absence of significant lipid absorption but it was associated with an increase of up to threefold in globulin concentration of lymph. In contrast there was little change in flow over the first 4 hr after feeding milk, although lymph flow increased up to 1· 5-fold at 5-6 hr, corresponding with the peak of lipid absorption.

Summary. Alloantibody was raised in PVG/c rats against DA rats. The calaholism of alioaniibody in normal PVG/c rats and PVG/c rats tolerant to DA rals was followed after intravenous injection. A haemaggluUnation assay was used to detect alloantibody activity. The half-life time of alloantibody IgG2a in the normal PVG/c rats was 10 days. On the other hand, in the PVG/c rats tolerant to DA rats, the half-life of alloantibody lgG2a varied. The rats could be divided into three groups. Group A; alloantibody IgG2a was eliminated from ihe circulation very rapidly. Group B: alloantibody lgG2a disappeared from the circulation relatively rapidly and was maintained at a low level in the plasma but then increased to a high titre. This peculiar pattern ofGroup B seems to be due to the endogenous production of alloantibody. In this case abrogation of tolerance took place. Group C: the pattern of elimination of this group was almost identical to that of normal rats.The biological significance of the plasma decay of alloantibody IgG2a in the normal and homograft tolerant rats has been considered. It is concluded from tbe present results that alloantibody might be important in some cases for tbe maintenance of homograft tolerance. INTRODUCTIONIn spite of the amount, class and the heterogeneous nature of immunoglobulin synthesised during an immune response, there appears to be very intricate regulation of immunoglobulin synthesis. This regulation could be mediated by several factors, such as the fate and presence of antigen, by cells involved in the immune response or antibody. In most cases following challenge with antigen, the level of antibody reaches a peak and decreases gradually in the circulation to fmally disappear. Some antigens such as bacterial lipopoly-