THE PANAMA CANAL 



159 



As soon as a boat passes the lower 

 lock gates they are closed behind it, and 

 water is let into that box or lock chamber 

 from the lock above until the same level 

 of water exists in the lower and middle 

 locks, the boat being lifted 28^ feet in 

 this operation. After that the gate sepa- 

 rating the lower and middle lock will be 

 opened and the boat will pass into the 

 second lock, the gates closed behind it, 

 and the process repeated, the boat being 

 lifted another 28^5 feet. That opera- 

 tion repeated once more will cause the 

 boat to float out on the level of. Gatun 

 Lake. 



The filling of the lower chamber of 

 Gatun lock for the first time is shown in 

 the picture on page 164. The gate on 

 which all the men are standing is called 

 the east gate or guard gate. These gates 

 were completed as soon as practicable 

 and then closed, so as to keep the sea out 

 of the locks while dredges were complet- 

 ing the excavations in the lock entrance, 

 thus not interfering with the work on 

 the other gates nor with the machinery 

 installation. 



PAINTING MOSQUITOES 



On both sides of the channel at Gatun 

 were extensive swamps. They were great 

 breeding places for mosquitoes, and in 

 digging the channel through the soft, 

 swampy bottom pipe-line dredges were 

 used. These dredges cut up the material 

 near the suction of the pumps, draw it in 

 with water, and force it long distances 

 through pipe-lines. In making the chan- 

 nel excavation those swamp areas were 

 built up high enough to enable the sani- 

 tary department to drain them. 



In 1912 Gatun had probably the great- 

 est influx of malarial mosquitoes in its 

 history; they came by the thousands. 

 The Gatun Lake was rising at that time, 

 and it was not known whether these mos- 

 quitoes were coming from that lake or 

 not; so the sanitary department deter- 

 mined to locate all the breeding places for 

 mosquitoes near Gatun, catch mosquitoes 

 at each place, and after painting them 

 turn them loose, and determine by the 

 color of the mosquitoes caught in Gatun 

 from what point they came. 



It was found that the largest breeding 



place was off to the west of the locks, in 

 an old swamp that had given no trouble 

 previously. A few mosquitoes had bred 

 in this place all the time, but there were 

 enough wild animals in the swamp to 

 supply food, so the mosquitoes were not 

 forced to migrate.* When salt water was 

 pumped into the swamp water, making 

 the mixture about 30 per cent salt, mos- 

 quitoes began to breed by the trillions. 



I went down there one morning to see 

 how the mosquitoes were caught and 

 painted. Walking along the edge of the 

 water, mosquito bars were seen sus- 

 pended from limbs tied up at the bottom. 

 They had thousands of mosquitoes in 

 them ready to be sprayed with a colored 

 liquid, and the sanitary inspector was 

 asked how he caught them. 



He said, "We have a more scientific 

 way, but this had to be done in a hurry. 

 We simply let the mosquito bar down, as 

 you would over a bed, left one side of it 

 open, and put a Jamaica negro in there 

 for bait." As soon as the mosquito bar 

 was full the bait was removed and the 

 end tied up. 



I saw some Jamaican negroes sitting 

 out in front, and I said to one fellow, 

 "John, were you the bait in that bar?" 

 and he replied, "Yes, boss ; that is the 

 easiest money I ever earned — ten cents an 

 hour for sitting there and doing nothing 

 but just inviting the mosquitoes in." 



THE DREDGING FLEET 



Just prior to the time that water was 

 let into Culebra Cut, a fleet of dredges 

 was brought up preparatory to removing 

 Cucaracha slide, the last one that ob- 

 structed the passage across the continent. 

 The picture on page 166 shows part of 

 the fleet assembled for passing through 

 the locks, and gives a good picture of a 

 pipe-line dredge, showing the cutter in 

 front. When this cutter is revolved, 

 those blades loosen the dirt, the intake of 

 the pump is just behind, and when the 

 water is drawn in by the pump it carries 

 in from 15 to 20 per cent of solid matter, 

 and the pump gives it velocity enough to 

 be carried from one-half to three-quar- 

 ters of a mile through a pipe. 



The entire dredging fleet is shown in 

 the picture on page 167. There were 



