120 RESOURCES OF CALIFORNIA. 



cities, is almost as regular in spring and fall as the move- 

 ments of migratory birds. Experience has proved that men 

 who can safely spend the winter in New Orleans cannot stay 

 there through one summer, without incurring greater danger 

 than soldiers usually do in a severe pitched battle. The pres- 

 ence of malarial diseases is generally proportioned to the 

 amount of rain, but in certain localities it depends on proxim- 

 ity to swamps, and the direction of the winds. Thus, if the 

 winds blow regularly through the summer in a certain dis- 

 trict from the westward, a town on low ground east of a 

 large swamp, in a hot summer, will be sickly, while another 

 town on the other side of the swamp may be quite healthy. 

 Let the wind shift for a few weeks, and the conditions will 

 change. If a high ridge runs through the sickly town, the 

 people there will be healthier than on the low land. A French 

 army that encamped on a malarial piece of ground, near Na- 

 ples, was suddenly reduced, by sickness, from 28,000 to 4,000 

 men. In 1809, a British army corps lost 10,000 men at Wal- 

 cheren, Netherlands, by malarial disease. It is highly dan- 

 gerous to spend a single night in the open air in portions of 

 the Campagna, near Rome. There are some very sickly 

 places on the Sacramento basin, to the leeward of the tule 

 swamps of ground flooded by water from ditches ; and the 

 introduction of extensive irrigation will injure the salubrity 

 of some districts now free from malaria. Yet irrigation will 

 not do more harm in the Sacramento-San Joaquin Valley than 

 it does in Lombardy, which is inhabited by a handsome, active, 

 and healthy race. 



89. Consumption. Consumption is, in most cases, the 

 growth of a cold, humid climate. In Massachusetts, from 20 

 to 25 per cent, of the deaths are by consumption ; in Philadel- 

 phia, 12 per cent. Boston has more consumption, in propor- 

 tion to its population, than any other place in the Union. It 

 is more common among those classes confined to the house 

 than those who work in the open air, the deaths by consump- 



