This fact has been made use of in the artificial bate “Oropon” (see Chapter VII.), in which extract of pancreas is combined with ammonium chloride, and some inert material. The effect of puering on the fatty matter in the skin is well known. The fat and grease are partially emulsified, and set free, so that they can be removed by scudding. This action is a most important one, and one in which artificial bates have hitherto been wanting. The emulsification of the fats is brought about by means of an enzyme either identical with, or closely resembling, lipase.[105] This enzyme is found in the pancreatic juice, and in the seeds of many plants. It brings about the emulsification of the fat by saponifying a portion of it, i.e. the fat is split up into glycerin[106] and a fatty acid, according to the equation-- C_{3}H_{5}(C_{18}H_{35}O_{2})_{3} + 3H_{2}O Stearin. = C_{3}H_{5}(OH)_{3} + 3(C_{18}H_{35}OHO) Glycerin. Stearic Acid. [105] Also known as steapsin, or pyolin (Allen, p. 357, vol. iv., Comm. Org. Analysis). [106] In the digestion of fat by dogs the glycerol produced is all absorbed before the ileum is reached, so that none exists in the excrement. (Levites, Chem. Soc. Abst. 1907, vol. iv. p. 891.) Lipase was one of the first enzymes in which the reversibility of the reaction was shown, i.e. it is not only capable of hydrolysing a fat, but also of causing the formation of one by the combination of the fatty acid and glycerin.[107] This explains why the reaction of such an enzyme is never complete. An equilibrium is reached just as with ordinary reversible chemical reactions like the precipitation of magnesium hydroxide by ammonia. [107] Another instance of the reversibility of enzyme action is the secretion of a peptolytic enzyme, by B. pyocyaneus; i.e. it has the power of synthesizing proteins, as well as of decomposing them. (Zak. Chem. Soc. Abst. 1907, p. 996.) Lecithin, and possibly other fatty compounds, are known[108] to be important auxiliaries in the ferment-like actions produced by toxins; cholesterol has a similar effect, and as this body is a constituent of dung, it may play some part in puering. Here, again, is a further problem awaiting investigation. [108] Chem. Soc. Annual Reports IV., 1907, p. 252. Loevenhart has shown that the bile salts, sodium cholate, and sodium glycocholate, greatly increase the activity of lipase, and Magnus found that synthetic bile salts have the same effect; such bodies are known as co-enzymes. I have shown that bile itself is not favourable to the bating action, but the bile salts, by stimulating the action of the fat splitting enzymes, are probably essential to the full action of the dung bate.