Xylan is the principal type of hemicellulose. It is a linear polymer of beta-D-xylopyranosyl units linked by (1-4) glycosidic bonds. In nature, the polysaccharide backbone may be added to 4-O-methyl-alpha-D-glucuronopyranosyl units, acetyl groups, alpha-L-arabinofuranosyl, etc., in variable proportions. An enzymatic complex is responsible for the hydrolysis of xylan, but the main enzymes involved are endo-1,4-beta-xylanase and beta-xylosidase. These enzymes are produced by fungi, bacteria, yeast, marine algae, protozoans, snails, crustaceans, insect, seeds, etc., but the principal commercial source is filamentous fungi. Recently, there has been much industrial interest in xylan and its hydrolytic enzymatic complex, as a supplement in animal feed, for the manufacture of bread, food and drinks, textiles, bleaching of cellulose pulp, ethanol and xylitol production. This review describes some properties of xylan and its metabolism, as well as the biochemical properties of xylanases and their commercial applications.

Degeneration of the parasympathetic ganglia in the heart and in the smooth muscle (esophagus, colon, and bronchi) is known to occur in Chagas' disease. The reflex bradycardia associated with acute elevation in systemic arterial pressure and the blocking of this reflex effect with atropine are used in this investigation to study vagotonic influences on the heart in patients with Chagas' disease. Failure to increase heart rate following administration of atropine observed in cases of chronic Chagas' heart disease is believed to be a functional disorder related to degeneration of the neuronal supply to the sino-atrial region of the heart. To the authors' knowledge this report provides the first existing physiological investigation concerning the cardiovascular system in Chagas' disease.

SUMMARY Haemodynamic responses to. sustained isometric exercise (handgrip at 30% of maximum voluntary capacity) were studied in 10 patients with Chagas's cardiopathy without previous or current heart failure. Five of the patients (group 1) had profound impairment of parasympathetic control of heart rate. They had no tachycardia in response to intravenous administration of atropine and no bradycardia during phase IV of the Valsalva manoeuvre. The other five (group 2) showed normal vagal regulation of heart rate, as judged by chronotropic responses to these tests.The heart rate change (mean (SD)) elicited by the handgrip test was significantly lower in group 1 (from 93 0 (14 1) to 95-0 (16-7) beats/min) than in group 2 (from 78-2 (15-8) to 92-8 (18 1)

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